1. Field of the Invention
The present invention relates to a clutching device, and more particularly to a clutching device for a crane and that has a low cost for maintaining the clutching device in a good operational condition.
2. Description of Related Art
To stop a crane encountering an overload situation, a brake device or a clutching device is always mounted on the crane. With reference to FIGS. 5 and 6, a conventional brake device for a crane comprises a main shaft (50), a transmitting gear (56), a pushing disk (53), a brake disk (54) and two brake pads (55). The main shaft (50) has a threaded portion (52) and a transmitting portion (51) with multiple teeth formed on the outer periphery of the main shaft (50). The transmitting portion (51) is connected to a lifting device (not shown) of the crane. The transmitting gear (56) and the pushing disk (53) are mounted on and engage with the threaded portion (52) of the main shaft (50). The transmitting gear (56) is connected to the shaft of a motor (not shown). The brake disk (54) is rotatably mounted between the transmitting gear (56) and the pushing disk (53). The brake pads (55) are respectively mounted on two sides of the brake disk (54) and respectively correspond to the transmitting gear (56) and the pushing disk (53). A securing collar (57) is securely attached to the main shaft (50) and abuts against the transmitting gear (56) to hold the transmitting gear (56) on the main shaft (50).
When the crane is in a normal use, the brake pads (55) are far from the transmitting gear (56) and the pushing disk (53). The main shaft (50) will be actuated to rotate by the motor with the transmission of the transmitting gear (56), and the lifting device of the crane will operate to lift an object.
When the loading to the crane exceeds the designated level of the crane, the main shaft (50) will rotate in reverse due to the large loading. The pushing disk (53) will move along the threaded portion (52) while the main shaft (50) reversely rotates and will abut against the corresponding brake pad (55) so as to push the brake disk (54) and the other brake pad (55) to abut against the transmitting gear (56). Consequently, a brake effect is provided.
However, the brake pads (55) in the conventional brake device are easily worn away after a period time of use. When the brake pads (55) are excessively worn away, a larger distance is needed for the pushing disk (53) moving to push against the brake pad (55). A brake effect cannot be promptly applied when the loading applied to crane exceeds the designated level.
With reference to FIGS. 7 and 8, a conventional clutching device for a crane comprises a main shaft (70), a transmitting gear (60) and two pushing disks (72). The transmitting gear (60) is rotatably mounted on the main shaft (70) and is connected to the shaft of a motor (not shown). Two clutching pads (61) are respectively mounted on two sides of the transmitting gear (60). The pushing disks (72) are securely mounted on the main shaft (70) and respectively abut the clutching pads (61). When the motor is switched on, the transmitting gear (60) is actuated to rotate. The pushing disks (72) will rotate with the transmitting gear (60) by means of the friction between the clutching pads (61) and the pushing disk (72), such that the main shaft (70) will rotate with the transmitting gear (60). Consequently, the lifting device connected to the main shaft (70) will be actuated to operate.
When the loading of the lifting device exceeds the designed level, i.e. the loading applied to the main shaft (70) is larger than the friction between the pushing disks (72) and the clutching pads (61), the transmitting gear (60) will rotate relative to the pushing disks (72). The pushing disks (72) and the main shaft (70) will not rotate with the transmitting gear (60), and the lifting device will not operate.
However, because the clutching pads (61) of the conventional clutching device are integrally mounted on the transmitting gear (60), the whole transmitting gear (60) must be replaced with a new one when even only one of the clutching pads (61) is worn away. The cost for maintaining the clutching device in a good operational condition is high, and it is wasteful to replace the transmitting gear (60) that just has a single clutching pad (61) excessively worn.
To overcome the shortcomings, the present invention tends to provide a clutching device to mitigate or obviate the aforementioned problems.
The main objective of the invention is to provide a clutching device and having a low cost for maintaining the clutching device in a good operational condition. The clutching device has a main shaft, a hub, a pushing disk and a transmitting gear. The hub is securely attached to the main shaft and has a shoulder formed on one end of the hub. The pushing disk is securely attached to the hub. The transmitting gear is rotatably mounted on the hub and is sandwiched between the shoulder of the hub and the pushing disk. The transmitting gear has a recess defined in each respective side of the transmitting gear, and two clutch pads are respectively received in the recesses in the transmitting gear and respectively abut the shoulder on the hub and the pushing disk. With such a clutching device, to replace the transmitting gear is not necessary while one of the clutching pads is worn away, such that the cost for maintaining the clutching device in a good operational condition is reduced.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.